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Owning a ... goldfish

Food and housing

The Aquarium

You should get the largest aquarium you can afford. Why? Because goldfish need a large surface area for oxygen to dissolve into the water from the atmosphere. The larger the tank, the greater the surface area and the more oxygen the fish have. The smallest suitable aquarium is 60cm x 30cm x 30cm (24in x 12in x 12in). Extra height will allow for taller plants and ornaments but no extra fish. To guage how many fish you can put in your aquarium, use this general rule - each 2.5cm (1in) of fish (excluding the tail) should be allowed 150cm2 (24 square inches) of water surface. Therefore a 60 x 30 x 30cm tank can hold 30cm of fish. BUT your fish will start small and grow to fit the tank. When calculating the number of fish that can stock your aquarium, allow for the ADULT size, not the junior size, of the fish.

You should NEVER keep goldfish in a bowl. As well as not providing enough oxygen, a bowl is basically like a toilet that never gets flushed - the ammonia levels (from the fish's waste) build up, turning the fish's environment into a sewer. Obviously the fish will not be at all healthy in this situation and will probably die.

The site of the aquarium is very important. Golfish are coldwater fish and the temperature of the tank should not exceed 23 Centigrade (74 Farenheit). It should not be placed in direct sunlight (so definitely NOT on a windowsill) or near any central heating pipes. A bedroom is is often a good site for the tank, since the temperature will be constant and there is also an electricity supply nearby. Take into account that a full tank (with gravel, plants, ornaments and several gallons of water) is VERY HEAVY (on average a full 60 x 30 x 30cm tank weighs 115kg) and must be placed on a sturdy structure, with a base of polystyrene pads to evenly distribute the weight. Often it is best to buy an aquarium stand.


Filtration is very important. A filter sieves out particles of waste and removes harmful pollutants from fish waste. Mechanical filters, in the form of a small black box which fits onto the side of the tank, work by drawing water across a foam block, which traps any dirt. They require regular cleaning in order to funtion 100%. Biological filters are placed on the floor of the aquarium and covered over by the gravel. They produce a continous flow of water through the gravel bed allowing beneficial bacteria to grow. These bacteria break down waste products into harmless compounds. A filter should be left running all the time.

Lighting is not essential (unless you have live plants in your aquarium) but a fishtank in the corner of a bedroom will not always get much sunlight. Most tanks come with a lid, which prevents evaporation, dust falling into the water and fish leaping out. These lids often have room for a light to be fitted to them. Lighting should be in the form of fluorescent tubes, NEVER normal household lightbulbs as these give off a lot of heat. Light is essential if you have live plants in your aquarium.

Most people use artificial plants for decoration. They are easy to fit and very realistic. Since real plants require light and are often eaten by the fish, they are harder to maintain. If lighting is provided, many hardy pond plants can be grown in the aquarium. These include pond weed (Egeria densa) and Vallis which should be planted in bunches 4-5cm into the gravel. To prevent uprooting, place larger stones around the base. Live plants produce oxygen for you fish.

To monitor the temperature of the aquarium you may want to get a thermometer. You will also need a net to hook out your fish when you need to. This may be due to illness, or maybe to move them to a different tank. To clean out the tank you will need a gravel cleaner.

Setting up the aquarium

This should be done at least two or three days before adding any fish. First, thoroughly wash the aquarium, gravel, rocks and ornaments etc. (without using any detergents) in a bucket using running water. The gravel will probably be quite dusty and will need rinsing a couple of times. Keep rinsing until the water remains clear after stirring.

Place the aquarium in the chosen position on a base of polystyrene pads. Make sure the tank is stable before filling it with gravel. The gravel should be 3-4 cm deep and should slope gently towards the front of the tank. This causes any debris to accumulate at the front where it can easily be removed. If using an undergravel filter you should place it on the base of the tank before adding the gravel.

If using a mechanical filter, position it near the back of the aquarium so that you can hide it with plants or rocks. Don't use limstone bearing rocks or cement in an aquarium as these partially dissove and cause the water to become alkaline, killing the fish.

Fill the aquarium with tap water from the cold tap. Water should either be left standing in a bucket for 24 hours to evaporate off the chlorine, or treated with shop-bought chemicals (e.g. Tetra Aquasafe) to make it safe. Either way, you MUST remove chlorine from any water you put into the tank.

If you want to add live plants, do so when the aquarium is one third full. Position them to hide the filter and provide hiding places for the fish. It is often best to position most of the plants at the back or near the edges so that there is an open area for the fish to swim in.

Once the tank is full, switch on the filter (and lights if you have any). This will remove any cloudiness from the water.

Two or three days after setting up the aquarium you can add one or two fish. Float the fish in their bag in the tank for 20 minutes to let the water in the bag gradually equall the temperature of the water in the tank. Undo the bag and let the fish swim out. These fish will help the tank environment to stabilise and mature. This process can take 2-3 weeks. Don't add any more fish during this period. After the 2-3 week period you can add more fish, usually only a couple every 1-2 weeks.

When first set up during the first week or so, the aquarium may become cloudy. This is caused by a bloom of microoragnisms which will clear in a couple of days, by which time the natural balance with surface-living bacteria will be reached. These nitrifying bacteria are found on plants, the gravel and the filter. If there are fish in the tank when it turns cloudy, the bloom of bacteria could be harmful and should be cleared away quickly via 25% water changes.


Fish should be fed small amounts of food twice a day, morning and evening. There are many dry foods available, either in flake or pellet form. These provide most of the nutrients a fish requires. It is a good idea to vary the type or brand of dry food your fish has, as each brand has slightly different ingredients which will fully complement the fish's diet. Make sure the food you choose is the right size for the fish you keep.

Live food can be fed. This includes Daphnia, Tubifex, bloodworms and mosquito larvae.

It is VERY important not to overfeed your fish.Uneaten food decomposes and pollutes the water. Only give the fish as much food as they will eat in 2-3 minutes. Remove any uneaten food. If they do not rise to the surface immediately, they are probably overfed.

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